1. Field of the Invention
This invention relates generally to the treatment of psychological disorders by stimulating appropriate regions of the thalamus, and more particularly to a method of interrupting pathological electrical activity of the brain by electrical stimulation of the corresponding nucleus or nuclei of the thalamus, and most specifically to the stimulation of the central median nuclei, intralaminar nuclei, and/or the central lateral nuclei.
2. Description of the Prior Art
Within the field of neurosurgery, the use of electrical stimulation for treating pathologies, including such disorders as compulsive eating, chronic pain, and movement disorders, such as Parkinson's disease essential tremor, has been widely discussed in the literature. It has been recognized that electrical stimulation holds significant advantages over alternative methods of treatment, for example lesioning, inasmuch as lesioning can only destroy nerve activity. In many instances, the preferred effect is to stimulate or reversibly block nervous tissue. Electrical stimulation permits such stimulation of the target neural structures, and equally importantly, it does not require the destruction of the nervous tissue (it is a reversible process, which can literally be shut off or removed at will).
Within this field, however, disorders manifesting gross physical dysfunction, not otherwise determinable as having emotional or psychiatric origins, comprise the vast majority of those pathologies treated by deep brain stimulation. A noteworthy example of treatment of a gross physical disorder by electrical stimulation is included in the work of Alim Benabid, and his research team, who have proposed a method of reducing, and in some cases eliminating, the temor associated with Parkinson's disease by the application of a high frequency electrical pulse directly to the subthalamic nucleus (see Neurosurgical Operative Atlas, Vol. 8, March 1999, pp. 195-207, Chronic Subthalamic Nucleus Stimulation For Parkinson's Disease; and New England Journal of Medicine, Vol. 339, October 1998, pp. 105-1111, Electrical Stimulation of the Subthalamic Nucleus in Advanced Parkinson's Disease).
Conversely, direct neuro-augmentation treatments for disorders which have traditionally been treated by behavioral therapy or psychiatric drugs, has been largely limited to peripheral nerve stimulation. A noteworthy example is the effort to control compulsive eating disorders by stimulation of the vagus nerve which has been described by Wernicke, et al. in U.S. Pat. No. 5,263,480. This treatment seeks to induce a satiety effect by stimulating the afferent vagal fibers of the stomach. For patients having weak emotional and/or psychological components to their eating disorders, this treament can be effective insofar as it eliminates the additional (quasi-normal) physio-chemical stimulus to continue eating. This is especially true for patients who exhibit subnormal independent functioning of these fibers of the vagus nerve. For compulsive eating patients who are not suffering from an insufficient level of afferent vagal nerve activity resulting from sufficient food intake, however, the over stimulation of the vagus nerve and potential resultant over abundance of satiety mediating chemicals (cholecystokinin and pancreatic glucagon) may have little effect. It has even been suggested that continued compulsive eating, despite overstimulation of the vagus nerve, may exacerbate the emotional component of the patient's disorder. This, therefore, begs the question, is vagus nerve stimulation useful in treating the psychological component of the disorder of compulsive eating, or is it simply a method of minimizing the additional, but natural, pressures to eat because of normal physical hunger. More generally, the question may be asked, is peripheral nerve stimulation of any kind the most appropriate method of treatment for disorders which are, at the core, the result of a pathology exhibited in the brain.
If the answer to this question is that the stimulation of a peripheral nerve can result in the release of a chemical which specifically counteracts the psychological pathology, for example if the release of greater amounts of cholecystokinin and pancreatic glucagon had a direct effect on the pathology exhibited in the brain, then, for that patient, the treatment will have a greater probability of success. If, however, as is most probably the case, the increase in the level of activity of the peripheral nerve does not result in the release of such a chemical, and therefore, has no effect on the area of the brain responsible for the emotional/psychiatric component of the disorder, then the treatment will have a much lower probability of success.
The impetus would, therefore, be to treat psychological disorders with direct modulation of activity in that portion of the brain which is causing the pathological behavior. Unfortunately, the ability to determine what region of the brain is responsible for a given patient's disorder is very difficult, and even more importantly, does not usually provide consistent patterns across a population of similarly afflicted patients. By this it is meant that the region of the brain which causes the behavioral pathology of one compulsive eating patient, for example, does not necessarily correspond in any way with the region of another compulsive eating patient.
In some manner, however, the determination of what regions of the brain are exhibiting pathological function must be determined. Fortunately, a method for determining precisely this has been developed by a number of researchers. Normal brain function can be characterized by four discrete frequencies of electrical output. Other frequencies are almost exclusively associated with pathology. The use of magnetoencephalography (MEG scans) has permitted quantificaion of electrical activity in specific regions of the brain. It has been proposed that MEG scans may be used to identify regions exhibiting pathological electrical activity. The resolution of the MEG scans of the brain are highly accurate (sub-one millimeter accuracy), however, correlating the MEG scan with MRI images for the surgical purposes of identifying anatomical structures limits the overall resolution for surgical purposes to a volume of 10 to 30 cubic millimeters. As stated above, however, simply identifying the regions of the brain which are exhibiting pathological electrical activity for a specific patient is not sufficient to generalize across a large population of patients, even if they are exhibiting identical disorders.
Fortunately, the architecture of the brain provides a substantial advantage in the search for a generic solution. This design advantage takes the form of a centralized signalling nexus through which many of the brain's disparate functions are channeled in an organized and predictable manner. More particularly, the thalamus is comprised of a large plurality (as many as one hundred, or more) of nerve bundles, or nuclei, which receives and channels nerve activity from all areas of the nervous system and interconnects various activities within the brain. The thalamus has been metaphorically described by some as the brain's equivalent of a highly organized train station. Many different train tracks come together, and many trains carrying many different cargos enter, however, if one has a schedule and a map, it is easy to find all the trains which carry coal (whether from Pennsylvania, West Virginia, Tennessee, or Arkansas), because all coal carriers are routed through the same tracks. It is this key which permits the treatment of common psychological disorders by brain stimulation of one specific area, rather than having to customize the (gross) placement of the stimulator for each patient.
It is therefore the principal object of the present invention to provide a more generically applicable method for treating certain psychological disorders.
It is further an object of the present invention to provide a fully reversible and adjustable method of treating certain psychological disorders.
It is still further an object of the present invention to provide a method of treating certain psychological disorders the effectiveness of which may be evaluated rapidly.
It is also an object of the present invention to provide a method of interventionally treating certain psychological disorders while minimizing the necessary pathological investigaion.